The inventive concept described herein generally relates to a semiconductor memory device, and more particularly to a semiconductor memory device having a delay lock loop with a wide frequency range and a delay cell current reduction scheme.
Similar to data transmission between a semiconductor memory device and a memory controller, an input and output method of transmitting data may have increased bus load and accelerated transmission frequency when transmission is in synchronization with a clock signal. It is thus important to temporally synchronize data with a clock signal. A phase lock loop (PLL) or a delay lock loop (DLL) may be used to temporally synchronize data with a clock signal.
A DLL is less affected by noise than a PLL, and is widely used in synchronous type semiconductor memory devices. Semiconductor memory devices operate at high speeds, and thus a DLL is required to perform locking operations at high speeds. A DLL may typically include a plurality of serially connected delay cells, and an external clock signal is received by one of the serially connected delay cells disposed at an input side of the DLL. Each of the serially connected delay cells delays the external clock signal for a predetermined period of time and outputs a delayed clock signal. In order to secure the characteristics of semiconductor memory devices operating at high speeds, each of the serially connected delay cells of the DLL has a relatively high consumption current, provides delay for a predetermined period of delay time, and is turned on so that the DLL may perform a locking operation at high speed.
Meanwhile, a DLL generally performs a locking operation over a wide frequency range according to an operation mode of a semiconductor memory device. When the semiconductor memory device operates at a low frequency, a greater number of delay cells of the DLL are turned on which consequently increases current consumption of the DLL, thereby increasing current consumption of the semiconductor memory device as a whole.
Therefore, there is a need for a DLL that performs a locking operation over a wide frequency range and with reduced current consumption.